1. Field of the Invention
The present invention relates to a printer, and more particularly, to a paper feeder of a printer which feeds a paper sheet from a paper feeding cassette or a manual paper feeding tray or returns the paper sheet of which one side has been printed in two-sided printing (duplex printing), to a paper conveyance path inside a printer body of the printer.
2. Description of the Related Art
Generally, a printer prints an image, which is formed and developed by a toner at an image forming unit, on a paper sheet which is fed from outside, and thus discharges the printed paper. Accordingly, the printer is generally provided with a paper feeding part which feeds the paper sheet to a paper conveyance path via the image forming unit of a printer body of the printer.
FIG. 1 is a sectional view schematically showing a conventional printing apparatus. A reference numeral 1 denotes a photosensitive belt unit, 2 is an exposure unit for forming a predetermined electrostatic latent image on the photosensitive belt unit 1, 3 is a developing unit for developing the electrostatic latent image of the photosensitive belt with color toners, 4 is a transfer unit for transferring the toner image of the photosensitive belt unit 1 onto a paper sheet, and 5 is a fusing unit for attaching the toner image on the paper sheet with heat and pressure.
The developing unit 3 includes four developers of yellow, magenta, cyan and black, and the transfer unit 4 includes a transfer drum 4-1 and a transfer roller 4-2. The fusing unit 5 includes a pair of fusing rollers 5-1, 5-2.
A main conveyance path 10 is defined inside a printer body of the printing apparatus, extending via the transfer unit 4 and the fusing unit 5 to a paper discharging tray. A paper feeding cassette 11 for a plurality of paper sheets is arranged at a lower side of the printer body. A pickup device 12 is disposed adjacent to the paper feeding cassette 11 and arranged to pick up the paper sheet from the paper feeding cassette 11 and to feed the picked-up paper to the main conveyance path 10.
In the conventional printing apparatus (printer) as constructed above, with a printing start signal input, the electrostatic latent image is formed on the photosensitive belt unit 1 by the exposure unit 2, and the electrostatic latent image is developed by the developing unit 3 and transferred to the transfer drum 4-1. Accordingly, the paper sheet is picked up by the pickup device 12 from the paper feeding cassette 11 and fed to the main conveyance path 10, and as the paper sheet passes between the transfer drum 4-1 and the transfer roller 4-2, the image, which is transferred onto the transfer drum 4-1, is transferred onto the paper sheet. Such transferred image is firmly attached to the paper as the paper sheet passes through the fusing unit 5, and the printed paper sheet is discharged out to the paper discharging tray.
The printers can have various paper storage and feeding means in addition to the paper feeding cassette 11 as mentioned above, such as a manual feeding tray (not shown) which is usually used for multi-purpose printing. The printer also has a paper returning part which inverts the paper printed on one side thereof and returns the paper back to the paper conveyance path.
In a manual paper feeding mode, the paper is placed on the manual feeding tray and fed to the main conveyance path 10 by a separate paper conveyance roller. In double-side printing or duplex printing, after the image is printed on one side of the paper sheet, the paper sheet is returned to the main conveyance path 10 by a separate paper returning device so that another image can be printed on the other side thereof.
In other words, the conventional general printers usually have many devices to feed the paper sheet to the main conveyance path 10, either from the paper feeding cassette 11 or the manual paper feeding tray or from the separate paper returning device for the duplex printing. That is, besides the pickup device and paper conveyance roller, many other paper conveyance rollers are required to feed the paper sheet to the main conveyance path 10.
As a result, a paper conveyance roller for automatic paper feeding, another paper conveyance roller for manual paper feeding, and a returning device for duplex printing are all required to be equipped in one printer, which makes the structure of the printer complex and also unnecessarily bulky. Also, the manufacturing cost of the printer becomes high.